refactor: adapt for telegraf v4.0 and v3.38

[EdJoPaTo]

The good thing about this: it is not breaking compatibility with 3.38

closes #106

Explanation:

• The example works with both telegraf 3.38 and 4.0 now
  • const {Telegraf} = require('telegraf') already works in 3.38
  • bot.launch() already works in 3.38 (bot.startPolling() was somewhat deprecated)
• the Typescript Types are kind of a hack to not be breaking:
  The import Path of MiddlewareFn changed with the update to v4 but Middleware is exported from the main export in v3.38 and v4.0. This results in slightly less good typings but as you normally only use bot.use(sessionLocal) you wont notice it.

Keep in mind that telegraf v4 requires NodeJS 12. But this is not a requirement of this library on its own so no (breaking) change needed there.

[wojpawlik]

• The import Path of MiddlewareFn changed with the update to v4

You can simply define it in the file:

type MiddlewareFn<C extends Context> = (ctx: C, next: () => Promise<void>) => Promise<void>

It's compatible with 3.38 and 4.x, and it should be forward-compatible with 5.x.

[EdJoPaTo]

You can simply define it in the file

Thank you for the suggestion @wojpawlik. Haven't thought about that.

Normally I would be against redefining types as this might end up as a potential bug later on. On the other side: MiddlewareFn is a very stable type. Not sure what it best here.

As bot.use(sessionLocal) is the only place where this is needed (which is a place where typings aren't that helpful as that's mostly never changes) I would just stick with Middleware and accept the slightly less good typings in a mostly never looked at place.

[wojpawlik]

I don't think you have a choice: making return type less specific is a breaking change.

Anyway, why did you change

const LocalSession = require('telegraf-session-local')

to

const LocalSession = require('../lib/session') // require('telegraf-session-local')

in README?

[wojpawlik]

I meant

Suggested change

	type MiddlewareFn<C extends Context> = (ctx: C, next: () => Promise<void>) => Promise<void>
	type MiddlewareFn<C extends Context> = (ctx: C, next: () => Promise<void>) => Promise<unknown>

Promise<void> should work too, but void's interactions are inconsistent.

[EdJoPaTo]

void is more precise than unknown?

[TemaSM]

Thank you guys for all of your work & conversation ❤️
I think we need also to adapt tests and examples to newer Telegraf version, and then I will merge this PR (after successfully running Travis CI tests)

PS> Happy New 2021 year!

[EdJoPaTo]

About the tests and Travis CI, why isnt travis listed in the checks?

[coveralls]

Coverage remained the same at 100.0% when pulling a248c83 on EdJoPaTo:telegraf-v4 into 0de45f6 on RealSpeaker:master.

[TemaSM]

Figured out, that Travis-CI moved from .org to .com, so I migrated project to .com and now it should works fine as before.

[wojpawlik]

Please release this on npm. Until then, I cannot recommend this library in Telegraf 4's readme.

[TemaSM]

@wojpawlik gonna release in 2 hours. How do you think, do we need to bump minor version to 2.1.0, or simply bump patch version to 2.0.1?

[EdJoPaTo]

Technically there is nothing new, just some fixes for the typings. So in that way, its a bugfix release.

Practically its a feature (which is not breaking) so I would tend to a minor version bump.